A copper-loaded two-dimensional silicon catalyst, a preparation method and application thereof

Abstract

The application discloses a kind of two-dimensional silicon catalysts loaded with copper and its preparation method and application, preparation method includes: under inert atmosphere, the mixture of two-dimensional silicon material and copper salt is annealed at 250~300 DEG C for 4~6h, and solid powder is obtained;Solid powder is washed, and copper salt not bonded with two-dimensional silicon material is removed;Under inert atmosphere, the product obtained by washing is annealed at 500~600 DEG C for 4~6h, and the two-dimensional silicon catalyst loaded with copper described is obtained.The two-dimensional silicon catalyst loaded with copper obtained by the application is mixed with polyethylene plastic, chloroaluminate ionic liquid / trichloromethane solvent and chlorinated tertiary alkane, and the reaction system is irradiated with light, which can drive polyethylene plastic depolymerization to obtain hydrocarbon compounds.The method of the application can realize the complete conversion of polyethylene plastic, obtain high-yield, high-value hydrocarbon compounds, and provide a new idea for green, value-added recycling of plastic waste.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalytic conversion and utilization of plastic waste, in particular to a two-dimensional silicon catalyst loaded with copper and a preparation method and application thereof. BACKGROUND

[0002] In recent decades, the global plastic production has soared. The annual plastic production reached an astonishing 390.7 million tons in 2021, a substantial increase of 4% over the previous year (Nat. Nanotechnol. 2023, 18, 687). The massive production of plastics has caused serious economic losses and greenhouse gas emissions, as most plastics are made from crude oil or natural gas. Globally, only 9% of plastic waste is recycled, and most of it is landfilled, incinerated or leaked into nature as waste, causing serious environmental and health disasters (Adv. Mater. 2021, e2100843). Therefore, it is necessary to design plastic waste management methods.

[0003] Among the plastic recycling methods, catalytic conversion is a promising technology that can convert plastic waste into value-added products while achieving environmental remediation and chemical production. However, its industrial practice is challenging, as the economic benefits of the products cannot recover the cost of the upgrading recycling process. In particular, polyethylene plastic, whose monomers are connected by extremely inert C-C bonds, is difficult to crack. Catalytic conversion of polyolefins usually requires harsh operating conditions, including high temperature, high pressure hydrogen and special reaction equipment, which greatly increases the cost of polyolefin upgrading recycling (J. Am. Chem. Soc. 2022, 144, 14269; Nat. Catal. 2018, 2, 46). Utilizing cheap and green solar energy to drive plastic conversion to obtain high-value hydrocarbon compounds is an effective method to alleviate the world's plastic waste crisis, and it is necessary to study it.

[0004] Traditional solar photocatalytic plastic conversion usually utilizes the photo-generated carriers of photocatalysts to drive the oxidative reductive depolymerization of plastics. Although these photocatalytic plastic conversion reactions can be carried out under mild conditions, their yields are extremely low (in μmol g cat. –1 h –1 on a horizontal plane), which inhibits its practical application. At the same time, photo-thermal catalysis as a new emerging plastic upgrading recycling method has attracted widespread attention for its clean energy input and excellent conversion efficiency.

[0005] Recently, the paper "Photothermal recycling of waste polyolefin plastics into liquid fuels with high selectivity under solvent-free conditions" (Nat. Commun. 2023, 14, 4242.) reported a photothermal system for polyolefin hydrogenolysis, which almost completely converted plastic waste in a short time (3 hours). However, in order to obtain a higher working temperature, the reaction requires a high light intensity of several tens of suns, so the reaction uses a solar concentrator, and the actual irradiation area is very small.

[0006] Recently, it has been reported that a polar environment can stabilize the ionic intermediates in the plastic cracking reaction, thereby reducing the temperature required for the reaction. This method has been applied to the thermochemical recycling of polyethylene terephthalate and polyethylene. As reported in the paper "Low-temperature upcycling of polyolefins into liquid alkanes via tandem cracking-alkylation" (Science 2023, 379, 807.), a high-polarity reaction environment was constructed using an ionic liquid solvent. They combined the endothermic cracking of polymer C-C bonds with the exothermic alkylation reaction. With isopentane as the reactant, the reaction completely converted low-density polyethylene (LDPE) into alkanes at a low temperature of 70℃.

[0007] Based on the above prior art, it is particularly important to design a solar-driven catalytic system to convert polyolefins into high-value hydrocarbons in order to solve the problems of high temperature, high pressure, hydrogen, and special reaction equipment in traditional thermal catalytic conversion of plastics, as well as the problem of low production rate in traditional photocatalytic conversion of plastics. SUMMARY

[0008] To solve the problems existing in the prior art, the present application provides a preparation method of a copper-loaded two-dimensional silicon catalyst, which has a simple catalyst preparation process, abundant raw materials, and low cost.

[0009] A preparation method of a copper-loaded two-dimensional silicon catalyst, comprising the following steps:

[0010] (1) Under an inert atmosphere, anneal the mixture of two-dimensional silicon material and copper salt at 250-300℃ for 4-6h to obtain a solid powder;

[0011] (2) Wash the solid powder to remove the copper salt that is not bonded to the two-dimensional silicon material;

[0012] (3) under inert atmosphere, annealing the product obtained in step (2) at 500-600℃ for 4-6h to obtain the copper-loaded two-dimensional silicon catalyst (Cu / 2D Si catalyst).

[0013] The mixture of two-dimensional silicon material and copper salt is first annealed at 250-300℃, in which process the copper ion precursor is combined with the two-dimensional silicon carrier. Then the obtained solid powder is washed to remove the copper salt not bonded with the two-dimensional silicon material. Finally, the obtained product is annealed at 500-600℃, in which process the Cu salt is decomposed at high temperature and the divalent copper ion is converted into zero-valent copper, obtaining a material with Cu nanoparticles embedded in the stacked two-dimensional Si structure, i.e. Cu / 2D Si catalyst. This catalyst can utilize the excellent dehydrogenation activity of metal Cu nanoparticles and the excellent light absorption and photo-thermal conversion of silicon nanosheets, thereby realizing the light-driven conversion of polyethylene.

[0014] Preferably, in step (1), the two-dimensional silicon material and the copper salt solution are ultrasonically mixed and stirred in an organic solvent, and then the organic solvent is removed to obtain the mixture of two-dimensional silicon material and copper salt.

[0015] The two-dimensional silicon material can be prepared by conventional methods such as stripping calcium silicide with hydrochloric acid and ultrasonic stripping of silicon powder.

[0016] Preferably, the copper salt includes one or more of copper chloride, copper sulfate or copper nitrate.

[0017] Preferably, in step (1), the molar ratio of silicon in the two-dimensional silicon material to copper in the copper salt is 1:0.03-0.2. If the copper loading is too low, the catalytic performance of the material will decrease. If the copper loading is too high, the loaded copper particles are prone to agglomeration, also reducing the catalytic performance.

[0018] Preferably, in step (2), the solid powder obtained in step (1) is washed with ethanol or water to remove the copper salt not bonded with the two-dimensional silicon material.

[0019] The application also provides a copper-loaded two-dimensional silicon catalyst prepared by the above preparation method. The Cu / 2D Si catalyst can absorb most of the sunlight and produce a local photo-thermal heating effect, realizing the complete catalytic conversion of polyethylene plastic and obtaining high-yield, high-value hydrocarbon compounds.

[0020] Preferably, the content of copper in the copper-loaded two-dimensional silicon catalyst is 3-20wt%. When the content of copper in the Cu / 2D Si catalyst is 6wt%, the catalytic performance of the Cu / 2D Si catalyst is optimal.

[0021] The application also provides the application of the copper-loaded two-dimensional silicon catalyst in the light-driven catalytic conversion of polyethylene plastic into hydrocarbon compounds.

[0022] Preferably, the application method is: under an inert atmosphere, mixing and stirring the polyethylene plastic, the copper-loaded two-dimensional silicon catalyst, the chloroaluminate ionic liquid / trichloromethane solvent, and the chlorinated tertiary alkane initiator, irradiating the reaction system with light to drive the depolymerization of the polyethylene plastic, and obtaining small molecule hydrocarbons.

[0023] The chloroaluminate ionic liquid / trichloromethane solvent used in the application can effectively swell the polyethylene plastic, so that the catalyst and the plastic substrate are in full contact; at the same time, the ionic liquid solvent can establish a high-polarity reaction environment, which is conducive to the stability of the carbocation intermediate in the polyethylene cracking reaction which also has high polarity; the initiator chlorinated tertiary alkane can generate a tertiary carbon ion by removing a chlorine atom, thereby providing the initial carbocation intermediate for the reaction. The two components in the Cu / 2D Si catalyst can capture the entire solar spectrum and produce a local photo-thermal heating effect, thereby driving the conversion of the plastic.

[0024] Preferably, the preparation method of the chloroaluminate ionic liquid / trichloromethane solvent is: mixing and stirring the ionic liquid, anhydrous aluminum chloride, and trichloromethane under an inert atmosphere.

[0025] Preferably, the ionic liquid includes 1-butylpyridinium chloride.

[0026] Preferably, the amount of the ionic liquid, anhydrous aluminum chloride, and trichloromethane is 6 mmol: 12 mmol: 3-6 mL. When the molar ratio of 1-butylpyridinium chloride to anhydrous aluminum chloride is 1:2, the performance of the sample is best. Trichloromethane can dilute the ionic liquid and is conducive to the swelling of the plastic and the dissolution of the product.

[0027] Preferably, the stirring speed is 600-1200 rpm, and the stirring time is 5-20 minutes.

[0028] Preferably, the chlorinated tertiary alkane includes one or more of chlorinated tertiary butane, chlorinated tertiary amyl, or chlorinated tertiary hexane.

[0029] Preferably, the amount of polyethylene plastic, copper-loaded two-dimensional silicon catalyst, chloroaluminate ionic liquid / trichloromethane solvent and chlorinated tertiary alkane is 200-1000 mg: 10-50 mg: 3 mL: 10-50 μL.

[0030] Preferably, the light source used in the light irradiation reaction system includes sunlight, focused sunlight or a xenon lamp.

[0031] Preferably, the irradiation light intensity of the light source is 100-500 mW / cm 2 , and the light irradiation time is 5-12 h. When the light intensity is 400 mW / cm 2 , the catalytic conversion effect is the best.

[0032] After 400 mW / cm 2 light irradiation for 6 h, the plastic conversion rate can reach 100%, and the product is a mixture of hydrocarbon compounds from C3 to C 26 , with a total yield of ~ 90%. Under light irradiation, the Cu / 2D Si catalyst can generate heat by non-radiative transition of photo-generated carriers. At 400 mW / cm 2 , the apparent temperature of the reactor is 55°C (without external heating source, the temperature is only caused by light source irradiation).

[0033] Compared with the prior art, the present application has at least the following beneficial effects:

[0034] (1) The present application first performs low-temperature annealing on the mixture of two-dimensional silicon material and copper salt, combines the copper ion precursor with the two-dimensional silicon carrier, then washes the obtained solid powder to remove the copper salt not bonded with the two-dimensional silicon material, and finally anneals the obtained product at high temperature to obtain a Cu / 2D Si catalyst with Cu nanoparticles embedded in the two-dimensional Si structure. The catalyst of the present application can utilize the excellent dehydrogenation activity of metal Cu nanoparticles and the excellent light absorption and photo-thermal conversion of silicon nanosheets to realize light energy-driven polyethylene conversion, and its preparation process is simple, the raw materials are abundant, and the cost is low.

[0035] (2) The present application can complete the conversion of polyethylene under low-intensity sunlight by using the prepared Cu / 2D Si catalyst, chloroaluminate ionic liquid / trichloromethane solvent. The conversion reaction is driven by pollution-free solar energy, and the reaction conditions are mild, which is conducive to large-scale application. At the same time, this method can realize complete conversion of polyethylene plastic and obtain high-yield and high-value hydrocarbon compounds. The present application provides a new idea for green and value-added recycling of plastic waste.

[0036] (3) The present application solves the problems of high temperature, high pressure, hydrogen and special reaction equipment of traditional thermal catalytic conversion of plastics, and also solves the problem of low production rate of traditional photocatalytic conversion of plastics, and the required light intensity of the new mode of photocatalytic conversion of plastics is significantly reduced, and the irradiation scale is larger. BRIEF DESCRIPTION OF DRAWINGS

[0037] The present application will be further described below in conjunction with the drawings and examples.

[0038] Figure 1 is the microstructure of the Cu / 2D Si catalyst prepared in Example 1 under a transmission electron microscope.

[0039] Figure 2 is the conversion rate of polyethylene plastic and the yield of hydrocarbons under 400 mW / cm 2 illumination using the catalyst of Example 1. DETAILED DESCRIPTION

[0040] Example 1:

[0041] (1) Preparation of copper-loaded two-dimensional silicon (Cu / 2D Si) catalyst

[0042] Put 1.0 g of calcium silicide powder into 100 ml of concentrated hydrochloric acid. Keep the temperature of the reactor between -15℃ and -20℃, and stir at a speed of 800 rpm under an inert atmosphere for 7 days. Then collect the solid product, wash it with anhydrous ethanol and dry it under vacuum to obtain two-dimensional silicon material. Disperse 0.50 g of two-dimensional silicon in an ethanol solution containing 0.86 g of CuCl2·2H2O. Ultrasonically treat the mixture for 30 minutes, and then remove the solvent at 80℃. Anneal the solid product at 300℃ for 5 hours under an inert atmosphere at a heating rate of 5℃ min -1 -1 to combine the metal precursor with the 2D Si carrier. Wash the powder with 30 ml of ethanol, centrifugally collect the solid product, and repeat three times to remove the metal precursor that is not combined with two-dimensional silicon. Anneal the obtained solid powder at 500℃ for 5 hours under nitrogen to obtain the Cu / 2D Si catalyst.

[0043] The microstructure of the Cu / 2D Si catalyst prepared in this example under a transmission electron microscope is shown in Figure 1 . As can be seen from Figure 1 , in the catalyst of this example, two-dimensional silicon exists in the form of nanosheet stacking, and the white bright spots are Cu nanoparticles confined in the stacked two-dimensional silicon.

[0044] (2) Preparation of chloroaluminate ionic liquid / trichloromethane solvent

[0045] In a container under a nitrogen atmosphere, add 3 mmol of 1-butylpyridine chloride, 6 mmol of anhydrous aluminum chloride, and 3 mL of chloroform. Stir the mixture thoroughly at 600–1200 rpm for 5–20 minutes in an ice-water bath to obtain a pale yellow chloroaluminate ionic liquid / chloroform.

[0046] (3) Solar-driven polyethylene conversion

[0047] Under an inert atmosphere, 200 mg of polyethylene plastic, 10 mg of Cu / 2D Si catalyst, and 10 μL of tert-butane chloroform initiator were added to 3 mL of aluminochloride ionic liquid / chloroform solvent. The mixture was stirred magnetically at 400 mW / cm². 2 Simulating sunlight irradiation of a catalyst, polyethylene plastic is depolymerized to obtain small molecule hydrocarbons.

[0048] The conversion rate of polyethylene plastic and the yield of hydrocarbons catalyzed by the catalyst in this embodiment are as follows: Figure 2 As shown. By Figure 2 As can be seen, in the conversion reaction of this embodiment, the cube data points represent the polyethylene conversion rate, which reaches 100% after 6 hours; the dot data represent the alkane yield, and the difference between the triangle and the dot represents the unsaturated hydrocarbon yield. It can be seen that the sum of the two yields reaches ~90% after 6 hours.

[0049] Example 2:

[0050] The difference between this embodiment and Embodiment 1 is that the light source is natural sunlight focused using a Fresnel lens. The optical power is controlled at 400mW / cm². 2 In this embodiment, the solar-driven polyethylene conversion reaction achieves 100% plastic conversion and 86% hydrocarbon yield after 6 hours of illumination.

[0051] Example 3:

[0052] The difference between this embodiment and Embodiment 2 is that the plastic is changed from polyethylene powder to shredded commercial low-density polyolefin plastic bags. The light power is controlled at 400 mW / cm². 2 In this embodiment, the solar-driven polyolefin plastic bag conversion reaction achieves a plastic conversion rate of 100% and a hydrocarbon yield of 91% after 6 hours of illumination.

[0053] Example 4:

[0054] The difference between this embodiment and Embodiment 2 is that the plastic is changed from polyethylene powder to shredded commercial high-density polyethylene plastic bottles. The light power is controlled at 400 mW / cm². 2In the solar-driven high-density polyethylene plastic bottle conversion reaction of the embodiment, the plastic conversion rate reaches 100% and the hydrocarbon yield reaches 80% after 12 hours of illumination.

Claims

1. Use of a two-dimensional silicon catalyst loaded with copper for the photocatalytic conversion of polyethylene plastic into hydrocarbon compounds, characterized in that, The preparation method of the copper-loaded two-dimensional silicon catalyst comprises the following steps: (1) under an inert atmosphere, annealing a mixture of two-dimensional silicon material and copper salt at 250-300 DEG C for 4-6h to obtain a solid powder; (2) washing the solid powder to remove the copper salt not bonded to the two-dimensional silicon material; (3) under an inert atmosphere, annealing the product obtained in step (2) at 500-600 DEG C for 4-6h to obtain the copper-loaded two-dimensional silicon catalyst.

2. Use according to claim 1, characterized in that, The molar ratio of silicon in the two-dimensional silicon material to copper in the copper salt is 1:0.03-0.

2.

3. Use according to claim 1, characterized in that, The content of copper in the copper-loaded two-dimensional silicon catalyst is 3-20wt%.

4. Use according to claim 1, characterized in that, The application method is as follows: under an inert atmosphere, mixing and stirring polyethylene plastic, copper-loaded two-dimensional silicon catalyst, chloroaluminate ionic liquid / trichloromethane solvent and chlorinated tertiary alkane; using light to irradiate the reaction system to drive the depolymerization of polyethylene plastic to obtain hydrocarbon compounds.

5. Use according to claim 4, characterized in that, The preparation method of the chloroaluminate ionic liquid / trichloromethane solvent is as follows: under an inert atmosphere, mixing and stirring 1-butylpyridinium chloride, anhydrous aluminum chloride and trichloromethane; the amount of 1-butylpyridinium chloride, anhydrous aluminum chloride and trichloromethane is 6mmol:12mmol:3-6mL.

6. Use according to claim 4 or 5, characterized in that, The amount of polyethylene plastic, copper-loaded two-dimensional silicon catalyst, chloroaluminate ionic liquid / trichloromethane solvent and chlorinated tertiary alkane is 200-1000mg:10-50mg:3mL:10-50μL.

7. Use according to claim 4 or 5, characterized in that, The light source used in the light irradiation reaction system includes sunlight, focused sunlight or xenon lamp.

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